The present invention is directed to a stage for moving a device. More specifically, the present invention is directed to a guideless stage for an exposure apparatus.
Exposure apparatuses are commonly used to transfer images from a reticle onto a semiconductor wafer during semiconductor processing. A typical exposure apparatus includes an illumination source, a reticle stage assembly retaining a reticle, a lens assembly and a wafer stage assembly retaining a semiconductor wafer. The reticle stage assembly and the wafer stage assembly are supported above a ground with an apparatus frame. Typically, the wafer stage assembly includes one or more motors to precisely position the wafer and the reticle stage assembly includes one or more motors to precisely position the reticle stage. The size of the images transferred onto the wafer from the reticle is extremely small. Accordingly, the precise relative positioning of the wafer and the reticle is critical to the manufacturing of high density, semiconductor wafers.
A typical wafer stage assembly includes a stage base, a first stage and a second stage. The stages move relative to the stage base to position the wafer. The first stage is used for relatively large movements of the wafer along a X axis. The second stage is used for relatively large movements of the wafer along a Y axis Existing wafer stage assemblies typically include a fixed guide with an air bearing that inhibits the first stage from moving along the Y axis and rotating about a Z axis relative to the stage base. With this design, if the stage base is rigidly connected to the reticle stage assembly, only 2 degrees of freedom, e.g. along the X axis and the Y axis, are required to maintain synchronization between the reticle stage assembly and the wafer stage assembly. U.S. Pat. No. 5,623,853, assigned to Nikon Precision Inc. illustrates an example of this type of stage assembly.
Unfortunately, if the stage base is not attached to the reticle stage assembly, rotation of the stage base will cause an alignment error between the reticle and the wafer. In this case, a strict requirement on the maximum rotation of the stage base is required to minimize the alignment error between the reticle and the wafer. Additionally, the fixed guide and air bearing combination generate a resonance that limits high bandwidth servo control of the first stage. This reduces the accuracy of positioning of the first stage and degrades the accuracy of the exposure apparatus.
In light of the above, one object of the present invention is to provide a stage assembly that can be moved with complete freedom in the planar degrees of freedom. Another object is to provide a stage assembly that can be precisely controlled in the planar degrees of freedom. Another object is to provide a stage assembly that is guideless in the planar degrees of freedom. Still another object is to provide a stage assembly having less resonances. Another object is to provide a wafer stage assembly that can correct alignment errors between the reticle and the wafer. Another object is to provide an exposure apparatus capable of manufacturing precision devices such as high density, semiconductor wafers.
The present invention is directed to a stage assembly for moving a device that satisfies these needs. The stage assembly includes a stage base and a first stage frame. The first stage frame moves the device relative to the stage base along a X axis, along a Y axis that is substantially orthogonal to the X axis, and around a Z axis that is substantially orthogonal to the X axis and the Y axis relative to the stage base. Stated another way, the first stage frame is guideless along the X axis, along the Y axis and about the Z axis (sometimes collectively referred to as xe2x80x9cthe planar degrees of freedomxe2x80x9d) and is not constrained along the Y axis, the X axis and about the Z axis. With this design, a pair of X movers and a first stage Y mover can precisely control the position of the first stage frame along the X axis, along the Y axis and about the Z axis. This allows for more accurate positioning of the device and better performance of the stage assembly.
Additionally, as a result of this design, there are no fixed guides that restrict the movement of the first stage frame in the planar degrees of freedom relative to the stage base. Thus, there are no resonances caused by fixed guides that influence the position of the first stage frame.
The X movers move the first stage frame along the X axis and about the Z axis while the first stage Y mover moves the first stage frame along the Y axis. The stage assembly also includes a second stage frame and a control system. The second stage frame moves relative to the first stage frame along the Y axis. The control system controls current to the X movers and the first stage Y mover.
Uniquely, the control system varies the amount of current to each X mover according to the position of the second stage frame relative to the first stage frame. As provided herein, the first stage frame and the second stage frame having a combined center of gravity that moves as the second stage frame moves relative to the first frame.
The control system controls current to each X mover based upon the location of the combined center of gravity. With this design, the X movers do not generate unwanted torque about the Z axis and the X movers move the first stage frame and the second stage frame in a smooth manner along the X axis.
The stage assembly also includes a second stage Y mover that moves the second stage frame along the Y axis relative to the first stage frame. Preferably, the stage assembly also includes a reaction stage and a trim mover that are coupled to the second stage Y mover. The reaction stage and trim mover transfer reaction forces from the second stage Y mover away from the first stage frame. A trim mover can be connected to the reaction stage.
The present invention is also directed to a method for making a stage assembly, a method for making an exposure apparatus, a method for making a device and a method for manufacturing a wafer.